This invention relates to fractionating apparatus, and is particularly concerned with novel fractionating structures particularly designed for use in non-adiabatic distillation.
One of the primary requirements of apparatus to be employed in non-adiabatic distillation is that both the liquid and gas phases be completely mixed during their travel through the fractionating zone. Another requirement is to provide a means of holding sufficient liquid within the fractionating zone to provide stability.
Various types of internal packing in the form of platefin constructions have been designed in the prior art in an effort to obtain greater fractionation efficiency. One such design is that disclosed in U.S. Pat. No. 2,885,195. In such construction, inclined corrugated plates with slots therein are provided for passage of the liquid-vapor mixture being separated, liquid reflux passing downwardly through the channels collecting in the upwardly inclined troughs formed by the corrugations until it overflows through the slots, the vapor passing upwardly through the channels via the slots impinging on the liquid film flowing from the respective slots.
In the "overflow" packing of the above patent, it was attempted to provide liquid holdup using a series of troughs. However, this construction results in a fractionating zone surface which has low surface to volume ratio and little liquid phase mixing. Further, the surface density of the type of material employed in the construction of the above patent is only about one-third that of conventional platefin constructions. Also, of particular significance, the construction of the above patent results in reduced heat transfer and has low structural strength resulting in a low pressure rating, generally only withstanding pressures not in excess of about 50 to 100 psi.
A fractionating zone operating in a true non-adiabatic manner behaves as a wetted wall condenser or evaporator so that if enough surface is provided, enough liquid holdup will be provided by the liquid film on the fractionator surface.
U.S. Pat. No. 3,568,461 to Hoffman discloses a fractionating apparatus or unit comprising two series of corrugated metal sheets disposed in vertical relation, each series of the two series of corrugated sheets or plates extending horizontally across the apparatus, the sheets of each series of corrugated sheets being substantially in vertical alignment, but with the second series of corrugated sheets offset from the first series of corrugated sheets. The result is the formation of a plurality of vertically disposed channels or paths formed by the vertically disposed cells of adjacent offset corrugations, with a portion of the alternate offset corrugations of alternate series of corrugations positioned in such vertical flow channels.
However, in the structural arrangement of the above patent, there is insufficient tortuous flow of vapor upwardly, and insufficient liquid holdup, to effect efficient mixing of liquid and vapor to provide highly efficient mass transfer for non-adiabatic fractionation.
It is accordingly an object of the present invention to provide fractionating apparatus particularly designed for efficient non-adiabatic fractionation, by the provision of means for efficient mixing of vapor and liquid, including continuous separation and intermixing of the adjacent vapor streams, and intermixing thereof with descending liquid, and also means for providing additional liquid holdup for stable operation.